In conventional camera design, the flash illumination source of the camera is off-axis with respect to the objective lens of the camera and illuminates from one angular orientation only. While this may be acceptable for the bulk of imaging applications, this arrangement is particularly troublesome for close-up imaging, such as in dental imaging and imaging of small objects in near distance. In close-up camera work, the conventional flash illumination arrangement often results in undesirable shadow and overexposure effects.
In response to the need for improved light distribution for minimizing shadows and other effects in close-up imaging, ring illumination has been developed. In ring illumination, a ring of light, ideally centered about the objective lens optical axis, is projected outward toward the imaging object. There have been a number of ring illumination solutions, including active ring light solutions that provide an alternate light source from the flash unit of the camera itself. Exemplary active ring light solutions include commercial products such as the Digi-Slave L-Ring Ultra LED Ring Light, from Digi-Slave, from SR Inc., Irving, Tex. This device threads onto the camera lens assembly and provides flash illumination from a circular array of bright LEDs. Another commercial solution is the Samigon Halo-Light FRL-1 Fluorescent Ring Light from Argraph Corp., Carlstadt, N.J. This device provides a continuous, bright ring of light when installed onto the camera lens. Other active ring light solutions are disclosed in U.S. Pat. No. 4,921,344 (Duplantis) and U.S. Patent Application Publication 2001/0010760 (Saito).
While such active ring light devices provide improved illumination for many types of close-up photography applications, there are some drawbacks. For example, many conventional ring lights require a separate source of electrical power, cabling for flash synchronization, and light sources of some type. Because of this, a conventional ring light system can be complex and costly. Another key disadvantage of such active ring light solutions relates to the suitability of the illumination provided to any particular camera. In most types of cameras, particularly cameras using a built-in flash mechanism, the spectral and intensity characteristics of the flash illumination are at least somewhat matched to the camera itself. Devices that substitute other types of light sources for flash illumination may indeed minimize shadows and other effects but, at the same time, may compromise image quality, particularly with respect to color balance. Other drawbacks with many conventional devices include excessive size and weight.
Using an alternative approach to the active ring light, various ring light solutions have been proposed for redirecting light from a conventional flash illumination mechanism into a ring light arrangement. For example:                U.S. Pat. No. 6,430,371 (Cho) discloses a ring light that uses a cluster of optical fibers to re-route light from the camera flash unit to an output ring.        U.S. Pat. No. 4,085,436 (Weiss) discloses an attachment with a translucent ring, having silvered reflective surfaces for distributing light around the ring. A plate member of this ring is clamped onto a separate electronic flash unit for redistributing light as ring illumination. The assembled and clamped ring light is then installed onto the camera lens.        U.S. Pat. No. 3,474,242 (Forrant) discloses a photographic ring light accessory that can be fitted around the camera lens, consisting of a somewhat horseshoe-shaped translucent light guide encased within a housing structure, the light guide ring having a gap at the base for accommodating its own flash source.        
While these solutions may provide light with spectral characteristics that are better suited to the individual camera type, drawbacks of complexity, cost, size, and usability remain. Ideally, for example, a ring light should be easy for a relatively unskilled photographer to carry, install, and use. Thus, it can be seen that there is a need for a ring light that is compact and inexpensive, fits readily onto a camera, allows straightforward use by an amateur photographer, and provides effective redistribution of light from the camera flash unit itself, without the complexity of a separate power source, light source, electrical connection, or synchronization components.